STPM Biology - chapter 2:Revision essay question 9

9. Explain how the following plant tissues are adapted for their functions.

Answer:

    i. Epidermis
       It is a protective tissue to protect inner tissue. Epidermis secrete cutine which forms a layer or waxy cuticle on the outer surface. This will reduces water loss by evaporation from the plant and entry of pathogens. It is transparent and allows light to reach the mesophyll layears of leaves for photosynthesis. Stomatal pores in epidermis allow gaseous exchange.

     ii. Parenchyma tissue
         It is the ground tissue of stems, roots and leaves of plants. When the cells are turgid and tightly packed they provide support for herbaceous plants. In leaves they form the mesophyll cells contain chloroplast and help carry out photosynthesis. They store starch, proteins and lipids. In a transverse section, the cell is usually round in shape. They are loosely packed together with many large intercellular air spaces to allow gaseous exchange. They are potentially meristematic and can form secondary meristematic tissue such as vascular cambium and cork cambium. The parenchyma cells in flowers and pericarp contain chromoplasts to attract pollinating agents and help in the dispersal of fruits and seeds.

   iii. Collenchyma tissue
        Cells are polygonal-shaped and elongated. The cells are closely packed together and no intercellular air spaces. It acts as a supporting tissue to provide the herbaceous plant with mechanical strength and flexibility. Some of the collenchyma cells contain chloroplasts which can carry out photosynthesis.

   iv. Sclerenchyma fibres
        It is elongated, polygonal-shaped with tapering ends. Mature sclerenchyma tissue consist consists of dead cells tightly packed with no intracellular air spaces. It have thick, lignified secondary cell walls impermeable to water, solutes and gases. The cells have no protoplasm with narrow empty lumen in center. Sclerenchyma acts as supporting tissue which provide the plants with mechanical strength and rigidity. The tapered ends of the sclerenchyma fibres overlap and interlock with another, further increasing their combined strength.

   v. Sclereids

       They have different shapes but are usually shorter than sclerenchyma fibres. They can be grouped into bundles, can form complete tubes located at the periphery or can occur as single cells or small groups of cells within parenchyma tissues. They consist of dead cells with thicker lignifid walls. Simple branching pits are present in the walls and called ramiform pits. It acts as protective tissue which gives strength and support to the plant structures or organs.

Assignment submitted by group 1  2011/2012 (IBM)

STPM Biology - chapter 2:Revision essay question 10

10. Compare prokaryotic cell and eukaryotic cell.  


Answer:

Organisms are classified into five kingdoms which are Prokaryotae, Protoctista, Fungi , Animalia and Plantae, there are two types of cell, prokayotic and eukaryotic cell.

The prokaryotic cell (mostly bacteria and cyanobacteria) has its DNA not enclosed by nuclear membranesand lack organelles bounded by a double membrane.The eukaryotic cell( include protoctists, fungi, animal and plant) have chromosomes surrounded by well-defined nuclear membrane. A prokaryotic cell's DNA is not surrounded by double-membraned nuclear envelope, the genetic material is a circular double strand of DNA. Most of the prokaryotes does not have plasmids, mitosis and meiosis does not occur in prokaryotes, therefore, there are no spindle formation too. Prokaryotic cell has simple and little organelles, it has 70S ribosome, food granules, pili and flagella etc. The prokaryote has mesosomes instead of mitochondrian which are present in eukaryotic cell. The cell are not compartmented and none of them is surrounded by an envelope, which mean the organelles are not arranged nicely. Thus, a prokaryotic cell does not function as efficient as a eukaryotic cell. with its simple structurem, only unicellular or filamentous prokaryotes exist.

There are different kind of eukaryote, there are unicellular, filamentous or truly multicellular organisms of eukaryotic cell. An eukaryote has chromatin which contain DNA and proteins called histones which will condense to form chromosomes during cell division. Mitosis, meiosis and spindle formation occur in eukaryotic cell. Eukaryotes have larger ribosomes(80S), the ribosomes may be attached to endoplasmic reticulum.eukaryotes have many specified organelles, the organelles are compartmented and more organized in order to function efficiently. There are enveloped bounded organelles such as nucleus, mitochondrian and chloroplast and single membrane bounded organelles such as Golgi apparatus, lysosomes, vacuoles, and microbodies.

Prokaryotes except blue green bacteria use mesosomes for respiration while eukaryotes use mitochondrian to undergo respiration. The eukaryotic cell is more complex than the prokaryotic cell. 

Assignment submitted by group 1  2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 8

     8. Describe the characteristic and the function of plasma membrane     

     Answer:

Plasma membrane is made up of double layer , diphospholipid bilayer which is hydrophobic tail and hydrophilic head.
Polar hydrophilic head is pointed toward the outside while hydrophobic tail is pointed toward inside.

Hydrophilic head can only dissolved in water while Hydrophobic tail can only dissolved in oil.
Plasma membrane is semi-permeable and regulate movement of substances in and out of cell.

 It separates the contents of cells from their external environment.

A plasma membrane included pore protein, cholesterol, glycoprotein, glycolipid, Channel protein

Cholesterol molecules help in stabilize the membrane structure and reduce the entry or exit of polar molecules through the membrane.

Pore protein and Channel protein enable the passive transport for molecules. Thus large molecules can pass through.

Also, it acts as receptor sites for recognizing certain molecules, either from other organs or from the external environment.
It attach the cells to adjacent cells or the extracellular matrix due to the presence of certain membrane proteins like integrins.

Assignment submitted by group 1  2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 7

7. Describe briefly the structure and functions of two organelles that are found in plant cell but not in animal cell.

Answer:                     

 Plant has cell wall and chloroplasts. Both of this organelle is not found in the animal cell. Cell wall is a rigid external cell wall that protects the plant and is only one cell thick. Cell wall is a non-living component located outside the plasma membrane and it is fully permeable. The cell wall made up a bundle of cellulose molecules known as microfibrils. Each microfibril composed about 3000 glucose residues condensed together and are held together by a matrix of pectin and hemicelluloses but the spaces between fibrils are not entirely filled with matrix. This lead to water, air and dissolved materials to pass freely through cell wall. The cell wall provides mechanical strength and skeletal support for the plant. The strong materials in cell wall has fibre-matrix system, the matrix provides stress to the fibres, which will have high ensile strength. The matrix also improves resistance to compression and protects them from infects of pathogen and possible chemical attack. The mature plant cell wall is made up of many layers. The first portion of young plant is created by primary cell wall. This layer is continues to grow. Fibrils in primary cell wall are arranged loosely. This arrangement of fibrils makes primary cell wall more elastic and allows for stretching during cell growth. The cells of soft tissues of plants have only primary cell wall and intercellular lamellae. After grow stops, cells become harder and more woody portions of the plant. This is due to the secondary wall is formed. Actually, the secondary wall is inserted between the plasma membrane and primary cell wall. The secondary cell wall is composed of compact layers or lamellae. In addition to cellulose, secondary wall also contains lignin, which is impermeable to water. As a result, leaving hard tube formed by their wall to functions as mechanical support and for internal transport. The cell wall also develops a coating of waxy cutin, the cuticle on the exposed epidermal surfaces to reduce water loss and risk infection.

Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 6

6. Describe the characteristic of meristematic tissue.

Answer: 

Tissue is defined as a collection of cells of similar structure and function to carry out one or more particular functions. Meristematic tissue is finding in living plant. Meristem consists of unspecialized and actively dividing cells that give rise to cells that differentiate into new tissue of the plant.  These cells are thin wall, isodiametric, abundant with cytoplasm and very small vacuoles. Thus, meristematic cells are compactly arranged within the tissue with no air spaces in between other plant tissues. Mitotic cell divisions occur throughout the meristem. New cells will undergo differentiate and grow so that become a specialized cells when mature. After then, differently specialized cells group together to become variety of plant tissues. Meristems are occurring at the tip of the shoot and root (apical meristem)and lateral meristems in older plant like cambium. Apical meristems are responsible for primary growth.

Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 5

b) With the aid of a labeled diagram, describe the structure and functions of Golgi apparatus.

Answer: 

All eukaryotic cells can find the Golgi apparatus. The Golgi apparatus located near the nucleus and consists of a stack of flattened, membranous bound sacs called cisternae. In a mammalian cell can consist of 5 to 6 cisternae while in plant cell can consists about 20 or more cisternae. From the above diagram (three dimension view) their outer convex surface called trans face while inner concave surface is called cis face. The cisternae at the cis face are differing from cisternae at the trans surface in terms of thickness. The cis face located near the rough endoplasmic reticulum and nucleus. The transport vesicles are bud off from the endoplasmic reticulum will fuse at the cis face of the golgi body. The trans face located far away from the nucleus and endoplasmic reticulum. It is sort the certain substances after modified such as lipids and proteins and then direct them to their destinations.

Function: Golgi apparatus receives, modified, processing and sorts secretory proteins arriving from cis face near the endoplasmic reticulum to other destinations. For example, the proteins synthesized by ribosome attached to rough endoplasmic reticulum pass into cisternal space and then transfer to the Golgi body as a transport vesicle. They are modified and processing to become a specific enzyme in order carry out certain reactions. After then, this specific enzyme is packing in secretory enzymes fused into trans face and bud off to different destinations. This secretory vesicle will be delivered to other organelles such as plasma membrane, where the content of vesicle is released to the outside of the cell by exocytosis.

Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 4

4. Distinguish bacteria chromosome from a eukaryotic chromosome.

Answer:

Chromosome is defined as a threadlike structure several to many which found in the nucleus. Chromosomes are composed of chromatin and carry genes, that is deoxyribonucleic acid (DNA).The eukaryotic cell such as animal cell and plant cell contains fins thread like structures called chromatin. Chromatin is made up of DNA and histone protein. The chromatin threads looked shorter and thicker during first phrase of mitosis when seen under the light microscope.  At this stage the chromatin is called chromosome. The chromosome is multiple linear which are DNA molecules wrapped around beads of histone protein. However, compared to the prokaryotic cells such as bacteria and cyanobacteria consists a single circular or “naked” DNA molecule compacted into nucleiod, that is, DNA not combine with protein.

Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 3

3. a) Discuss how erythrocyte and its pigments are related to their function.

   b) Explain why haemoglobin molecules are not found in blood plasma.

Answer:

a) -  Erythrocytes function to transport oxygen and some carbon dioxide.

    - Erythrocyte are small,biconcave discs with a diameter of 7-8 µm.This increases     the surface area per volume ratio and allow oxygen to diffuse quickly into or out of the cell.

  - The elastic membrane of the erythrocytes enable the erythrocytes to squeeze through the narrow blood capillaries.

 - The cells  move in a single line and are closer to the capillary to diffuse rapidly into the cell.

- Te erythrocyteshave no nucleus,no organelles such as mitochondria and ER.

- There is more space to contain haemoglobin,increasing the amount of oxygen which can be carried by he erythrocytes,There are about 250 million haemoglobin molecules in each erythrocyte.

- Since the erythrocyte are small cells,the haemoglobin molecules are not far from the plasma membrane and its source of oxygen.

- Haemoglobin has a quartenary structure.It is made up of four polypeptide chains,each chain has a haem group containing iron.Each molecule of haemoglobin can therefore combine with four oxygen molecules.

- Some carbon dioxide (10%) can combine with haemoglobin to form carbaminohaemoglobin which is carried by the erythrocytes.

b)  ~  If haemoglobin were suspended in the plasma rather than enclosed within erythrocytes,the blood would become too viscous for the heart to the heart to pump the blood through the blood vessels.

   ~  Haemoglobin would also affect the solute potential In the blood.

~  Membranes of Bowman’s capsule in the nephron allows only proteins of molecular weight below 68000 to pass.The haemoglobin molecules are smaller than 680000 threshold molecule weight.If present in the plasma,the haemoglobin can pass through the fitration membrane and be lost in the urine.

Assignment submitted by group chee tian 2011/2012 (IBM)

STPM Biology - chapter 2: Revision essay question 2

               2. Explain how the structure of

i)                   Parenchyma, and

ii)                 Xylem tissue sre suited to their function

Answer:

·        Parenchyma cells are unspecialized cells with variety of functions.

·        They are isodiametric cells and function as [packaging tissue and storage tissue.

·        They have thin cellulose cell wall which is permeable, permit passage of materials.

·        The cell walls are transparent and permit entry of light in photosynthesis cells.

·        Cells are loosely packed with many large intercellular spaces.This provide spaces for storage of substances.Entry of water causes vacuole to expand and cells to become turgid,giving support to herbaceous plant.

·        Choloroplast present in some cells permit photosynthesis to take place.

·        Leucoplasts act as storage of starch.

·        Choromoplast present in some cells e.g. petals attaract insects for pollination.

·        Parenchyma can become specialized to carry put specific functions e.g. epidermis,mesophyll,endodermis and aerenchyma.

   ii)   -  Xylem vessel consist of long,hollow xylem  elements joined end to end.

-         When mature,the end walls dissolved to form continuous tube.

-         The xylem walls are impregnated with lignin of different patterns.

-         The lignified wall strengthened the vessels and prevent them from collapsing when water flows through the vessel under high pressure.

-         Xylem vessel consist of dead cell with no protoplasm.More water can flow through the hollow vessels with less obstruction.

-         The lignified wall prevent water escaping except through certain region e.g. pit to the surrounding living cells.

-         Vessels are thin and narrow,help to pull water up by capillarity.


Assignment submitted by group chee tian 2011/2012 (IBM)

STPM Biology - chapter 4(old syllabus) chapter 6 (new syllabus): Revision essay question 4

4.Explain the process that occurs in Calvin Cycle in plants. [10]

Answer:

-Occurs in stroma of chloroplast
-Does not require sunlight
-RuBP fixes CO2 to form unstable 6C compound
-The fixation is catalysed by RuBP carboxylase -This unstable compound split immediately into 3PG     - 3PG is then phosphorylated into 1,3-BPG
-ATP is used

-Reduction of 1,3-BPG to G3P by NADPH
-To produce 1 molecule of G3P, 3 molecules of CO2 are required

-3 molecules of CO2 will produce 6 molecules of G3P

-Whereby only 1 molecule of G3P will be used to produce sugar

-While the other 5 molecules remain in Calvin cycle-Rearrangement of the 3 carbon G3P producing RuBP and can be used to fix with CO2 again catalysed by RuBP carboxylase

STPM Biology - chapter 4(old syllabus) chapter 6 (new syllabus): Revision essay question 3

3. Explain the differences between cyclic and non-cyclic photophosphorylation


Answer:

cyclic phosphorylation

- involve PS1 only

- only ATP produced

- no photolysis of water

- final acceptor not NADP, so no production NADPH

non-cyclic phosphorylation

- involve PSI and PSII

- ATP and NADPH produced

- involved photolysis of water

- final acceptor is NADP,so there is production NADPH

STPM Biology - chapter 4(old syllabus) chapter 6 (new syllabus): Revision essay question 2

2. Describe the process of light reaction which occurs in green plants. [8]Answer:

▪ when photon of light reach photosystem II, the light energy is absorbed by chlorophyll in photosystem II.   ▪ The aborption of light by chlorophyll causes electrons to be excited to higher energy level   ▪ electron hole found in photosystem II, as a result of excited electron must be filled   ▪ this is done by splitting of water molecules by water splitting enzyme that give rise to electron that fill in the hole   ▪ oxygen gas is released in the process as well▪ As electron cascade dowm electron transport chain, ATP is produced ▪ the production of ATP is called photophosphorylation because it is generated through light reaction.▪ when photon of light reach photosystem II, the light energy is absorbed by chlorophyll of photosystem I  ▪ absorption of light energy by chlorophyll causes electron to be excited to higher energy level and is accepted by electron acceptor ▪ electron hole is filled by electron cascading down from photosystem II ▪ electron acceptor in photosystem I passes the excited electron to Fd  and then to NADP+ reductase ▪ NADP+ reductase  passes the electron to NADP+ to produce NADPH ▪ NADPH will provide reducing power for synthesis of sugar in Calvin cycle.

STPM Biology - chapter 4(old syllabus) chapter 6 (new syllabus): Revision essay question 1

1.With the aid of labelled diagram, show the structure of chloroplast. [2]


Answer:

STPM Biology - chapter 1: Reision essay question 34

34. Into which two groups can the nitrogen-containing bases that form DNA and RNA be classified? What is the criterion used in that classification?

Answer:

The nitrogen-containing bases that form DNA and RNA are classified as pyrimidine and purine bases.

By the analysis of the structural formulae of those nitrogen-containing bases it is possible to realize that three of them, cytosine, thymine and uracil, have only one nitrogenized carbon ring. The others, adenine and guanine, have two nitrogenized associated carbon rings.

Assignment submitted by C.L., Ooi, T. T., Tan, K. Y., Ho, S.S., Aiu, X. H., Wong  2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 33

33. What are nucleic acids? What is the historic origin of this name?


Answer:


DNA and RNA, the nucleic acids, are the molecules responsible for the hereditary information that commands the protein synthesis in living beings. The name “nucleic” derives from the fact that they were discovered (by the Swiss biochemist Friedrich Miescher, in 1869) within the cell nucleus. In that time it was not known that those substances contained the hereditary information.


Assignment submitted by C.L., Ooi, T. T., Tan, K. Y., Ho, S.S., Aiu, X. H., Wong  2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 32

32. Which are the nucleotides “portions” that bind in the formation of nucleic acids? What is meant by the 5’ and 3’ extremities of nucleic acids?


Answer:

The phosphate group of one nucleotide binds to the pentose of the other nucleotide and so on to make the polynucleotide chain.

Each extremity of a DNA or RNA chain can be distinguished from the other extremity according to their terminal chemical entity. The phosphate-ended extremity is called 5’-extremity and the pentose-ended extremity is called 3’-extremity. So DNA or RNA chains can be run along the 5’-3’ way or along the 3’-5’ way. These ways are important in several biological functions of DNA and RNA since some reactions specifically occur following one way or the other way.

Assignment submitted by C.L., Ooi, T. T., Tan, K. Y., Ho, S.S., Aiu, X. H., Wong  2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 31

31. Explain how the structure of collagen and haemoglobin are related to their function.



Answer:

The structure of collagen , which is a fibrous potein,consists of a primary structure of a repetitive tripeptide sequence that forms long chains and may run parallel to each other. In the secondary structure has three unbranched polypeptide chains linked to one another via cross bridges and forming a triple helix. These cross bridges involve strong coxalent bonds that help provide structural support to the collagen molecule,thereby making it resistant to stretching .Hence,collagen has an important structural role in providing physical strength to connective tissue such as tendons .While, the structure of haemoglobin ,which is a conjugated protein ,consists of sequences of amino acids forming four polypeptise chains that twist and fold into a compact shape and has haem as the prosthetic group.Two chains are a chains and the other two are b chains held together by hydrophobic interactions , hydrogen and ionic bonds. Haemoglobin has a quartenary structure, with each haem group contains a ferrous iron atom that is able to carry an oxygen molecule. Therefore, each human haemoglobin molecule is capable of carrying 4 oxygeb molecules , making it an efficient respiratory pigment involved in oxygen transport. 
Assignment submitted by C.L., Ooi, T. T., Tan, K. Y., Ho, S.S., Aiu, X. H., Wong  2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 30

30. Describe the main ways in which a globular protein differs from DNA.


Answer:

 

Globular protein	DNA
1.It has polypeptide chains with irregular sequences of amino acids.	1.It is a polynucleotide chain consisting of deoxyribose, phosphoric acid and organic base.
2.Its shape is a compact globule of polypeptides.	2.Its shape is a double helix with the two chains running antiparallel to each other.
3.Its a chemically less stable and its activity is affected by factors such as its concentration, pH and temperature.	3.It is chemically very stable and relatively unaffected by temperature, concentration or pH.
4.Each molecule of the same type of globular protein has a specific sequence.	4.DNA molecules may vary with different sequences of organic bases.
5.It is incapable of undergoing replication.	5.It is capable of undergoing replication.
6.It can be secreted out of cells and transported to various parts of the body such as in the case of enzymes or hormones.	6.Its found almost entirely in the nuclei of cells and it is not transported or secreted.
7.It is involved in various body systems such as the digestive system,the endocrine system and the immune system.	7.Its role is genetic inheritance where its sequences of bases codes for the genes that determines specific characteristics .

 

Assignment submitted by C.L., Ooi, T. T., Tan, K. Y., Ho, S.S., Aiu, X. H., Wong  2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 29

29. Describe the important of water soluble vitamins in human metabolism. [7]

Answer:

A)     Water soluble vitamins are vitamin B complex and vitamin C/ ascorbic acids.

@ Vitamin C/ ascorbic acids

-anti-scurvy.

-coenzyme.

-antioxidant/ detoxification.

@ Vitamin B

~B1/ Thiamine- helps release energy from carbohydrate/ decarboxylation.

~B2/ Riboflavin-component of FAD and FMN/ coenzyme.

~B3/ Niacin/ Nicotinic acids- component of NAD+ and NADP+.

~B5/ Panthotenic acid-component of coenzyme A.

~B6/ Pyridoxine- coenzyme in amino acid/ protein metabolism/ transamination.

~B12/ Cobalamine/ Cyanocobalamine- coenzyme in nucleic acids metabolism/ maturation of red blood cell.

~Biotin-coenzyme in metabolism.

~Folic acid/ Folate-coenzyme in nucleic acid and protein metabolism/ formation of red blood cell.

Assignment submitted by L.E., Teh, E.L., Wong, Tan Findy 2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 28

28. Describe 4 properties which render water to be an important medium for life. [8]

Answer:

A)     # Solvent

-water is a polar/ dipolar/ charged molecules

-solubilize most of biological molecules/ medium for biological reaction/ ionic solids/ nutrient substances.

-due to the hydrogen bonding.

# High heat capacity/high latent heat of vaporization.

-good in maintaining against temperature fluctuation/ stabilize temperature.

-high boiling point.

-Vaporization leads to the cooling effect.

# High surface tension

-formation of plasma membrane/ micelle.

-cohesion and adhesion forces for movement of water up a capillary.

# maximum density of water at 4ºC/ ice float on water.

-water increases in volume and reduces in density as temperature drops

-this ensure aquatic organism to survive in freezing water/ ice is a insulator of heat.

# low viscosity

-acts as lubricant/ low resistant for movement.

Assignment submitted by L.E., Teh, E.L., Wong, Tan Findy 2011/2012 (IBM)

STPM Biology - chapter 1: Reision essay question 27

27. Give 4 types of proteins and their functions in the living organisms. [4]

Answer:

A)   Types of protein function:

-catalytic enzymatic to catalyze biological reactions.

-to transport oxygen and carbon dioxide in the blood circulation (haemoglobin).

-to transport other substances to other part of the cells or within the cells.

-regulatory/ messenger/ hormone coordination of cellular activities through messenger molecules (insulin).

-storage for molecules required by the organism (ovalbumin-storage for amino acid; calmodulin-storage for calcium; ferritin-storage for iron).

-structural for support of organisms (cocoon, hair, skin, keratin).

-immune/ defense/ protection against diseases ( antibodies).

-receptor response of cells to chemical stimuli.

-contractile and motor, for movement and mobility (actin & myosin).

-act as hydrolytic enzymes.

-visual protein for vision.

Assignment submitted by L.E., Teh, E.L., Wong, Tan Findy 2011/2012 (IBM)